Linking Fundamental Investigations and Engineering Results for Extinguishment of Fires on Solid Material

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Abstract - Vlachos CTS - 9710413 This is an investigation of flame extinction of fires on solid materials occurring because the energy feedback to the surface decreases either by direct cooling of the surface or by inerting of the oxidant stream by a thermal or chemical agent. The study uses modern continuation methods for numerical calculation of stationary-state solutions in chemical reaction systems. Numerical results are interpreted with a novel sensitivity analysis, simple physical models for flame extinction, and standard asymptotic analysis. Gaseous combustion dynamics is separated from the surface energy balance by simulating the pyrolyzing material with a porous gaseous burner at a constant temperature in which a fule such as methane or ethylene burns with the oxidant flow. One isssue examined is when critical conditions for extinction, such as dimensionless fuel supply, are independent of the Damkohler number. The flame heat feedback to the surface is calculated as a function of mass supply rate for various dilutions of the fuel and/or oxidant streams by chemically inert or active agents and for various strain rates. Both convective and radiative heat feedback are included. Empirical methods for extinguishing fires have been used since prehistoric times. In the last thirty years, sophisticated models for extinction in gaseous flames have been developed, but little of this can be applied to fires on solid surfaces. Details of pyrolysis chemistry for most solid materials of practical interest are unknown. At present, no general, robust strategy exists to characterize extinction of solid fires under varioius ambient flow and environmental conditions. Such a strategy is outlined in this project; it integrates state-of-the-art fluid-phase and chemistry models and nonlinear systems theory with available experimental data and measurement techniques for extinction.